Bone plate and resilient screw system allowing bi-directional assembly

ABSTRACT

Bone screws and bone plates are provided that offer the surgeon the ability to either assemble the screws to the plate, or the plate to the screws, depending on the surgeon&#39;s preference and the patient&#39;s circumstances. The bone screws and bone plates of the present invention include a combination of geometric configurations that allow the screws and plates to fit together from different assembly directions. Additionally, the bone screws and bone plates can include material resilience features to allow expansion/contraction during assembly to allow bi-directional attachment to one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/335,539 filed on Dec. 31, 2002 and entitled “Bone Plate and ScrewSystem Allowing Bi-Directional Assembly,” which is hereby incorporatedby reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to bone fixation devices used inorthopedic and spinal surgeries for stabilizing and immobilizing bonefragments. More particularly, this invention relates to a bone plate andscrew system that allows both a plate first or anchors first approach toimplanting the bone plate.

BACKGROUND OF THE INVENTION

Bone fixation devices are useful for promoting the proper healing ofinjured or damaged vertebral bone segments caused by trauma, tumorgrowth, or degenerative disc disease. These external fixation devicesimmobilize the injured bone segments to ensure the proper growth of newosseous tissue between the damaged segments. External bone fixationdevices such as these often include internal bracing and instrumentationto stabilize the spinal column to facilitate the efficient healing ofthe damaged area without deformity or instability, while minimizing anyimmobilization and post-operative care of the patient.

One type of external bone fixation device is an osteosynthesis plate,more commonly referred to as a bone plate, that can be used toimmobilize adjacent skeletal parts such as vertebral bones. Typically,the fixation plate is a rigid metal or polymeric plate positioned tospan bones or bone segments that require immobilization with respect toone another. The plate is fastened to the respective bones, usinganchors such as bone screws, so that the plate remains in contact withthe bones and fixes them in a desired position. Anterior cervicalplates, for instance, can be useful in providing the mechanical supportnecessary to keep vertebral bodies in proper position and bridge aweakened or diseased area such as when a disc, vertebral body or spinalfragment has been removed. These anterior cervical plates usuallyinclude a rigid bone plate having a plurality of screw openings. Theopenings are either holes or slots that allow for freedom of screwmovement. The bone plate is placed against the damaged vertebral bodiesand bone screws are used to secure the bone plate to the spine, usuallywith the bone screws being driven into the vertebral bodies.

Currently, bone screws and bone plates allow either a plate firstconstruction or an anchors first construction. That is, some bone screwsand bone plates are constructed such that the bone plate is placed ontothe intended area to be fixed, and then the bone screws are insertedthrough the plate to secure the plate to the bone segments. In otherbone plate and screw systems, the screws are inserted into the bonesegments first, then the plate is secured to the screws. One benefit ofbeing able to apply a bone screw and plate system using such an anchorsfirst approach is that the plate is not positioned in a manner that willblock the surgeon's view of the implantation site. The surgeon istherefore able to better position the plate and manipulate around thepatient's anatomy during implantation.

It would be desirable to provide bone screws and bone plate systems thatare both easy to use and capable of bi-directional assembly using eithera plate first or anchors first construction. Such a system would allowthe clinician the flexibility to use either a plate first or an anchorsfirst approach with the same bone screw and bone plate during surgery.One benefit of being able to apply a bone screw and plate system usingan anchors first approach is that the plate is not positioned over thesurgical site before inserting the screws, and so the plate does notobstruct the surgeon's view when implanting the screws. While it ispossible to achieve flexibility and the aforementioned benefits with atwo-part bone screw comprising a threaded nut and bone screw or post, asingle-component bone screw is more desirable because it does notrequire intraoperative assembly and therefore has enhanced ease of use.

SUMMARY OF THE INVENTION

The present invention achieves the aforementioned goals by providingsystems of single-component bone screws and bone plates that offer thesurgeon the ability to either assemble the screws to the plate, or theplate to the screws, depending on the surgeon's preference and thepatient's anatomical conditions. With this invention, the surgeon isgiven intraoperative flexibility regarding the approach taken whenapplying the system, allowing the clinician to use either a plate firstor anchors first approach with the same screws and plate. The bonescrews and bone plates of the present invention include a combination ofgeometric configurations that allow the screws and plates to fittogether from different assembly directions. Additionally, the bonescrews and bone plates can include material resilience features to allowexpansion/contraction during assembly to enable bi-directionalattachment one another. The various geometric configurations of thepresent system allow the bone plate and screws to accommodate differentpatient anatomies as the natural bones settle after implantation. Thegeometric configurations also provide the bone plate and screw systemwith selective biomechanical properties such as toggling, translation,and/or rotation to facilitate bone growth and healing.

In one exemplary system of the present invention, the bone plate andscrew system comprises a bone plate for stabilizing bone segments, ascrew configured for insertion into bone, and a resilient locking memberfor securing the bone plate to the screw. The bone plate has a firstsurface and a second, bone-contacting surface that is opposed to thefirst surface, and an aperture extending through the first and secondsurfaces. The aperture has a predefined shape and size, and isconfigured to receive the bone screw.

The bone screw of the present embodiment has a head region at a proximalend and an elongated body extending from the head region to a distal endof the screw. In one aspect of the invention, the head region is definedby a top flange, a bottom flange, and a groove extending therebetween,while the elongated body includes a threaded portion configured forinsertion into bone. Additionally, the aperture of the bone plateincludes a seating groove for capturing the resilient locking member.

The resilient locking member secures the bone plate to the implantedscrew, and is sized and shaped to mate with the groove of the screw. Forexample, the resilient locking member can be an expandable snap ring.The entire system can be assembled together using either a plate firstor an anchors first approach, with the latter being desirable for theadvantages previously mentioned. Preferably, the entire system can beassembled together using both a plate first and an anchors firstapproach to provide the benefits associated with bi-directionalassembly.

In another aspect of the invention, the bone screw of the present systemhas a head region defined by an upper surface, a lower surface, and asidewall extending therebetween and connecting the upper and lowersurfaces. The head region is located at a proximal end, while anelongated body extends from the head region to a distal end of thescrew. The elongated body includes a threaded portion for insertion intobone. To secure the bone plate to the screw, a resilient locking memberis provided having a top surface, a bottom surface, and an outer wallextending therebetween and connecting the top and bottom surfacestogether.

The resilient locking member also includes a channel extending about itsinner circumference, the channel being sized and shaped to capture thehead region of the screw. Also, the resilient locking member can have atop surface which extends along a downward slope from an outer edge toan inner edge of the top surface, and a bottom surface which extendsalong an upward slope from an outer edge to an inner edge of the bottomsurface. The chamfered features help to facilitate assembly of the boneplate and screw system.

In another exemplary system of the present invention, the bone plate andscrew system comprises a bone plate for stabilizing bone segments and aresilient screw configured for insertion into bone. The bone plate has afirst surface and a second, bone-contacting surface that is opposed tothe first surface, and an aperture extending through the first andsecond surfaces. The aperture has a predefined shape and size, and isconfigured to receive the resilient screw. The aperture can becountersunk on either the first or second surface of the bone plate, orboth, to accommodate a direct engagement with the bone screw.

The resilient screw of the present embodiment has a head region at aproximal end and an elongated body extending from the head region to adistal end of the screw. The elongated body includes a threaded portionfor insertion into bone. In one aspect of the invention, the head regionis defined by a top flange, an bottom flange, and a groove extendingtherebetween. At least one of the top and bottom flanges of the screw isresilient, such that the bone plate and screw system can be assembledtogether using either a plate first or an anchors first approach, withthe latter approach being desirable to provide the benefits associatedwith an anchors first construction to the system. More preferably, thesystem can be assembled bi-directionally using both a plate first and ananchors first construction.

The present system can optionally include an attachment member forsecuring the bone plate to the screw. The optional attachment member canbe sized and shaped to mate with the groove of the resilient screw.Further, the attachment member can be configured to be captured within aseating groove provided within the aperture of the bone plate.Attachment member can have a top surface which extends along a downwardslope from an outer edge to an inner edge of the top surface, and abottom surface which extends along an upward slope from an outer edge toan inner edge of the bottom surface. These chamfered surfaces help tofacilitate assembly of the bone plate and screw system.

In another aspect of the invention, the resilient bone screw of thepresent system has a head region having a compressible diameter, thehead region being defined by an upper surface, a lower surface, and asidewall extending therebetween and connecting the upper and lowersurfaces. The head region is located at a proximal end, while anelongated body extends from the head region to a distal end of thescrew. The elongated body includes a threaded portion for insertion intobone. To secure the bone plate to the resilient screw, an optionalattachment member can be provided having a top surface, a bottomsurface, and an outer wall extending therebetween and connecting the topand bottom surfaces together. The attachment member also includes achannel extending about its inner circumference, the channel being sizedand shaped to capture the head region of the resilient screw.

In yet another exemplary system of the present invention, the bone plateand screw system comprises a resilient bone plate for stabilizing bonesegments, and a screw configured for insertion into bone. The bone platehas a body including a first surface and a second, bone-contactingsurface that is opposed to the first surface. At least one resilientaperture having a predefined shape and size extends through the firstand second surfaces. The aperture is configured to cooperate with arelief slit extending therefrom to allow the aperture to expand andcontract to receive the bone screw. The relief slit can extend into arelief hole, or another aperture. The resilient bone plate of thepresent embodiment can include a plurality of resilient apertures,relief slits and relief holes.

The bone screw of the present embodiment has a head region at a proximalend and an elongated body extending from the head region to a distal endof the screw. In one aspect of the invention, the head region is definedby a top flange, a bottom flange, and a groove extending therebetween,while the elongated body includes a threaded portion for insertion intobone. The bone plate and screw system can be assembled together usingeither a plate first or an anchors first approach, with the latterapproach being desirable to provide the benefits accorded with ananchors first approach as previously mentioned. Preferably, the systemcan be assembled bi-directionally using both a plate first and ananchors first construction.

In other features of the present invention, each of the plurality ofapertures can be shaped like a hole or an oblong slot. The apertures aresized and shaped to receive screws configured to be inserted into bone.The screws can be used to anchor the bone plate to bone segments. Eachof the screws has a head region at a proximal end. In one instance, thehead region is defined by a top flange, a bottom flange, and a groovelocated between the top and bottom flanges and extending about thecircumference of the head region. In another instance, the head regionis defined by an upper surface, a lower surface, and a sidewallextending therebetween and connecting the upper and lower surfaces. Anelongated body which includes a threaded portion extends from the headregion to a distal end of the screw. In yet another instance, the headregion includes a flange and a groove extending about the circumferenceof the head region. The body of the screw extends from the groove downto the distal end.

The bone screws of the present invention can be provided with achamfered proximal surface of the top flange and/or a chamfered distalsurface of the bottom flange. At least one of the top and bottom flangescan also have a compressible diameter to allow bi-directional attachmentto the bone plate. For instance, the top and bottom flanges can includeat least one vertical relief slit extending therethrough. To allow foranchors first construction in this embodiment, at least the top flangeis resilient. Further, each screw can have an open head region, with athreaded bore extending from an upper surface of the head region. Athreaded cap can be provided that is configured to engage with thethreaded bore of the head region. The threaded cap can be capturedwithin a nested region of the countersunk rim of the apertures. Whenthreaded onto the head region, the threaded cap provides a smoothprofile to the bone plate and screw system while at the same timelimiting movement of the screw with respect to the bone plate.

To secure the bone plate to the screws, a plurality of resilient lockingmembers are provided with the bone plate and screw system of the presentinvention. The resilient locking members are sized and shaped to matewith the grooves of the screws, and enable locking engagement of thebone plate to the screws. Each of the resilient locking members isconfigured to be disposed in a seating groove within the apertures ofthe bone plate. The resilient locking members can comprise expandablesnap rings, or C-rings.

In one exemplary embodiment of the present invention, the seating grooveof the bone plate includes a ratcheted edge along a side thereof. Aresilient locking member comprising an expandable snap ring having anotched edge is also provided. The ratcheted edge of the seated grooveis configured to mate with the notched edge of the expandable snap ring.The expandable snap ring can further include a channel extending aboutits inner circumference for capturing the head region of the screw.Alternatively, the expandable snap ring can be configured to nest aroundthe groove of the screw. Such features provide the clinician with evenmore flexibility with respect to the manner of implementation.

The present invention also provides a bone screw which can be assembledto a bone plate in a plate first or anchors first approach. The bonescrew comprises a head region at a proximal end of the bone screw. Thehead region is defined by a top flange, a bottom flange, and a grooveextending therebetween about a circumference of the head region. Anelongated body extends from the head region to a distal end of thescrew. The elongated body can include a threaded portion configured forthreading into bone. The proximal surface of the top flange and thedistal surface of the bottom flange can be chamfered to facilitate theinsertion of a locking member over the head region and into the groove.Preferably, at least one of the top and bottom flanges has acompressible diameter. Further, at least one of the top and bottomflanges includes at least one vertical slot extending through theflange. The head region can also include a threaded bore extending froma proximal end thereof.

Also provided is a method for assembling the bone plate and screwsystems described above using an anchors first approach, wherein atleast one screw is inserted into a bone segment to be fixed. A taperedpost can be attached to the screw to facilitate alignment and placementof the bone plate over the bone screw. If a resilient locking member isto be used with the system, the locking member should be captured withinthe seating groove of the bone plate prior to assembly. Next, the boneplate (with the optional resilient locking member) is disposed over thetapered post and aligned with the implanted screw. The bone plate isslid down the tapered post and onto the implanted screw. The taper ofthe post will facilitate the expansion of either the bone plate apertureor the resilient locking member, depending on which system is beingused. After the aperture or locking member has been maneuvered so thatit is disposed around the groove of the implanted screw, the taperedpost can then be removed from the screw, leaving an assembled bone plateand screw system.

Further features of the invention, its nature and various advantages,will be more apparent from the accompanying drawings and the followingdetailed description of the drawings and the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is an exploded view of a bone plate and screw system of thepresent invention;

FIG. 1B is a perspective view of the bone screw with the locking memberand cap of FIG. 1A;

FIG. 1C is a cutaway view of an aperture of FIG. 1A having a screw,resilient locking member and cap nested therein;

FIG. 2A is an exploded view of the bone plate and screw system of FIG.1A showing a plate first construction;

FIG. 2B is a detailed view of an aperture of FIG. 2A;

The invention can be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is an exploded view of a bone plate and screw system of thepresent invention;

FIG. 1B is a perspective view of the bone screw with the locking memberand cap of FIG. 1A;

FIG. 1C is a cutaway view of an aperture of FIG. 1A having a screw,resilient locking member and cap nested therein;

FIG. 2A is an exploded view of the bone plate and screw system of FIG.1A showing a plate first construction;

FIG. 2B is a detailed view of an aperture of FIG. 2A;

FIG. 3 illustrates a method of assembling the bone screw and platesystem of FIG. 1A;

FIG. 4A is a view of another embodiment of the bone plate and screwsystem of the present invention;

FIG. 4B is a detailed view of an aperture and locking member of FIG. 4A;

FIG. 5A illustrates a step in the method of applying the bone plate andscrew system of FIG. 4A;

FIG. 5B illustrates another step in the method of applying the boneplate and screw system of FIG. 4A;

FIG. 6A illustrates yet another step in the method of applying the boneplate and screw system of FIG. 4A;

FIG. 6B illustrates a completely assembled and implanted bone plate andscrew system of FIG. 4A;

FIG. 6C is a cross-sectional view of an aperture of FIG. 6B;

FIG. 7A is a perspective view of another embodiment of a bone screw andresilient locking member of the present invention;

FIG. 7B is a side view of the bone screw of FIG. 7A;

FIG. 7C is an enlarged view of the resilient locking member of FIG. 7A;

FIG. 8A is a side view of even another embodiment of a bone screw of thepresent invention;

FIG. 8B is a cross-sectional view of the bone screw of FIG. 8A alongwith the resilient locking member of FIG. 7C;

FIG. 8C is a cross-sectional view of the bone screw of FIG. 8A;

FIG. 9A is a perspective view of a bone screw for yet another embodimentof a bone plate and screw system of the present invention;

FIG. 9B is a bottom-up view of the bone screw of FIG. 9A;

FIG. 9C is a top-down view of the bone screw of FIG. 9A;

FIG. 10A is a perspective view of another embodiment of a bone screw andattachment member of the present invention;

FIG. 10B is a perspective view of another embodiment of the bone screwof FIG. 10A;

FIG. 10C is a perspective view of the bone screw of FIG. 10A;

FIG. 10D is a side view of the bone screw and locking member of FIG.10A;

FIG. 10E is a cross-sectional view of the bone screw and locking memberof FIG. 10D along lines A-A;

FIG. 10F is a cross-sectional view of the bone screw and locking memberof FIG. 10E along lines B-B;

FIG. 11 is a perspective view of a bone plate for yet another embodimentof the bone plate and screw system of the present invention;

FIG. 11B is a bottom-up view of the bone plate of FIG. 11A;

FIG. 11C shows the bone plate of FIG. 11A with a bone screw;

FIG. 11D is a perspective view of the bone screw of FIG. 11C;

FIG. 11E is a cross-sectional view of the bone plate and screw of FIG.11C along lines C-C;

FIG. 12A is a perspective view of another embodiment of a bone plate ofthe present invention;

FIG. 12B is a top-down view of the bone plate of FIG. 12A;

FIG. 12C is a top-down view of the bone plate of FIG. 12A with a screw;

FIG. 12D is a bottom-up view of the bone plate and screw of FIG. 12C;

FIG. 12E is a cross-sectional view of the bone plate and screw of FIG.12C;

FIG. 13A is a schematic view of another embodiment of a bone plate ofthe present invention;

FIG. 13B is a schematic view of even still another embodiment of a boneplate of the present invention;

FIG. 14A is a perspective view of yet another embodiment of a bone plateof the present invention; and

FIG. 14B is still another perspective view of an embodiment of a boneplate of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides bone screws and bone plates that offerthe surgeon the ability to either assemble the screws to the plate(i.e., plate first approach), or the plate to the screws (i.e., anchorsfirst approach), depending on the surgeon's preference and the patient'sanatomical situation. The bone screws and bone plates of the presentinvention include a combination of geometric configurations that allowthe screws and plates to fit together from different assemblydirections. Additionally, the bone screws and bone plates can includematerial resilience features to allow expansion/contraction duringassembly for enabling bi-directional attachment to one another.

Turning now to the drawings and particularly to FIG. 1A, an exemplarybone plate and screw system 10 for stabilizing bone segments of thepresent invention is shown. In the illustrated embodiment, the system 10includes a bone plate 20 defined by a first surface 22 and a second,bone-contacting surface 24 that is opposed to the first surface 22. Thebone plate 20 can optionally be convexly curved along its length,enabling the bone plate 20 to conform to the curvature of naturalvertebral bones. A plurality of apertures 26 extend through the firstand second surfaces 22, 24 of the bone plate 20. Each of the apertures26 has a predefined shape and size. For instance, each of the apertures26 can be shaped like a hole or an elongated, or oblong, slot asillustrated. In addition, the rim 30 of the apertures 26 can becountersunk on the first surface 22 of the bone plate 20.

As shown in FIG. 1A, each of the apertures 26 is configured to receiveone of a plurality of screws 40 configured to be inserted into bone. Thescrews 40 can be used to anchor the bone plate 20 to the particular bonesegments that require fixation. Each of the screws 40 has a head region46 at a proximal end 42. The head region 46 is defined by a top flange48, a bottom flange 54, and a groove 60 located between the top andbottom flanges 48, 54 and extending about the circumference of the headregion 46. The top flange 48 is defined by an upper surface 50 and alower surface 52, while the bottom flange 54 is defined by an uppersurface 56 and a lower surface 58. An elongated body 62 which includes athreaded portion 64 extends from the head region 46 to a distal end 44of the screw 40.

To secure the bone plate 20 to the bone screws 40, a plurality ofexpandable and compressible locking members 70 are provided with thepresent bone plate and screw system 10. Each of the locking members 70is resilient and, as illustrated in FIG. 1B, sized and shaped to matewith the groove 60 of the bone screws 40. As further shown in FIGS. 1Aand 1C, each of the locking members 70 is configured to be disposed in aseating groove 28 within the aperture 26. The seating groove 28 liesbetween the first and second surfaces 22, 24 and runs about thecircumference of the aperture 26 of the bone plate 20 to enable lockingengagement of the bone plate 20 to the bone screws 40. While notillustrated as such, it is contemplated that the locking members canhave a top surface that extends along a downward slope from an outeredge to an inner edge of the top surface, and a bottom surface thatextends along an upward slope from an outer edge to an inner edge of thebottom surface. These chamfered features help to facilitate assembly ofthe bone plate and screw system.

As depicted in FIGS. 1A-1C, it is contemplated that each of the lockingmembers 70 can comprise a C-ring or expandable snap ring for placementaround the groove 60 of the bone screws 40 and for capture within theseating groove 28 of the apertures 26. The locking members 70 arecapable of expanding and contracting to snap into the groove 60 of thebone screws. Each of the locking members 70 can also include a cutoutportion 72 extending around the inner circumference for seating the topflange 48 of the bone screw 40. As shown in detail in FIG. 1C, thecutout portion 72 enables the top flange 48 of the head portion 46 tosit securely within the locking member 70, with the lower surface 52 ofthe top flange 48 resting against the cutout portion 72. Depending onits thickness, the locking member 70 can optionally include a cutoutportion on its underside (not shown) mirroring the cutout portion 72 onthe upper side to accommodate the bottom flange 54 of the bone screw 40.When surrounding the groove of the screw 40 and nested within theseating groove 28, the locking member 70 allows for translation ineither direction and settling of the screw in to maintain compressionacross the bone/graft interface.

As shown in FIG. 1C, which depicts a cutaway view of the aperture ofFIG. 1A directly above, top flange 48 can include a chamfered uppersurface 50 and bottom flange 54 can include a chamfered lower surface58. The chamfered surfaces 50, 58 of the bone screw 40 help facilitatethe placement of the locking member 70 over the head region 46 and intothe groove 60. The top flange 48 can also include a tool-engaging recess66 extending vertically therethrough for engaging an insertion tool (notshown). In addition, each screw 40 can optionally have an open headregion including a threaded bore 68 extending from an upper surface ofthe head region 46. The threaded bore 68 can be configured as either ahexagonal bore or a threaded bore, for example, to engage an insertertool such as a post.

As an additional feature of the bone plate and screw system 10 of thepresent invention, a plurality of threaded caps 80 are provided, each ofwhich are rigid and configured to engage with the threaded bore 68 ofthe head region 46. The threaded cap 80 can include a cap head 82 withan elongate, threaded body 84 extending therefrom. The threaded body 84is configured to complement and mate with the threaded bore 68 of thebone screw 40. When threaded onto the head region 46 as illustrated inFIG. 1B, the threaded cap 80 provides further securement of the boneplate 20 to the bone screw 40.

The threaded cap 80 can have a tool-engaging bore 86 extending from anupper surface of the cap head 82 for engaging an inserter tool (notshown). As illustrated in FIG. 1C, the tool-engaging bore 86 cancomprise a hexagonal bore. It is understood, however, that tool-engagingbore 86 can be configured with any suitable geometry, for example, as athreaded or hexagonal bore. The cap head 82 has a thickness that matchesthe depth of the countersunk or depressed rim 30 surrounding theapertures 26 on the first surface 22 of the bone plate 20. A nestedregion 32 along the countersunk or depressed rim 30 of the oblongapertures 26 helps capture and stabilize the threaded cap 80 within theaperture 26. The nested region 30 has surface features that includenotches 34 at discrete locations along the rim 28. The notches 34conform to the outer surface of the threaded cap 80, which together withthe cap 80 allows the screw 40 within the oblong aperture 26 to be fixedat a discrete position. This feature is especially useful in spinalcorrection procedures where the bone segments to be fixed areselectively compressed or distracted over time, by moving the headregion 46 of the screw 40 and its associated cap 80 along the nestedregion 32. As applied in FIGS. 1A and 1C, the cap head 82 sits flushagainst first surface 22 of the bone plate 20 to provide a smoothoverall profile, avoiding damage to soft tissue surrounding the implantsite.

The present system 10 is designed to allow versatile use of thedifferent components, i.e., bone plate, screws, locking ring, cap, etc.in a number of combinations and configurations. Depending on thecombination of components assembled, the bone screws 40 can be rigidly(i.e., no toggling, translation or rotation), semi-rigidly (i.e.,rotation and toggling but no translation), or dynamically (i.e.,translation and optionally rotation) fixed with the system 10 of thepresent invention. Thus, the surgeon or clinician using the presentinvention can select and provide for desirable biomechanical propertiesintraoperatively. The ability to control these biomechanical propertieswith the present system 10 is most desirable where the surgeon has toaccount for the natural settling of bone post-surgery.

In the present embodiment shown, apertures 26 are configured to allowrelative fixation of the screws 40. In the case of the oblong apertures26, the screws 40 are able to slide within the oblong aperture 26 untillocked into place using the threaded cap 80 which would be capturedwithin the surface features of the countersunk rim 30, e.g., notches 34of the nested region 32 around the oblong apertures 26. The threaded cap80, when captured within the notches 34 of the nested region 32, wouldthus restrict translation and/or rotation of the screw 40 within theaperture 26. In contrast, without the threaded cap 80, the screw 40 heldby the locking member 70 alone would still be able to translate androtate, but not toggle.

FIG. 2A depicts the bone plate and screw system 10 as applied with aplate first approach. Preferably, the resilient locking members 70 arealready captured within the seating groove 28 of the apertures 26 of thebone plate 20 prior to assembly. The plate 20 with the captured lockingmembers 70 is placed on the bone surface to be fixed. Next, the bonescrews 40 are inserted into the bone segments using a conventional bonescrew applicator (such as inserter tool 100 as shown in FIG. 3) throughthe captured locking member 70. The bone screws 40 can be pre-engaged tothe applicator prior to this step. Using the screw applicator/post toinsert the threaded portion 64 of the bone screw 40 through the capturedresilient locking member 70, the surgeon can apply force to slide thebottom flange 54 of the screw 40 past the expandable locking member 70until the head region 46 is nested within the locking member 70 andaperture 26 as shown in FIG. 1C. The resilient locking member 70, beingcaptured within seating groove 32 of the aperture 26, thus secures theplate 20 to the bone screw 40 as the bone screw 40 is screwed into thebone segment to be fixed. Finally, the threaded cap 80 can be threadedinto the threaded bore 68 of the bone screw 40 to provide rigid fixationof the bone screw 40 to the bone plate 20. Where the aperture 26comprises an elongated or oblong slot, the nested region 32 along thecountersunk rim 30 of the aperture 26 helps stabilize and lock in thethreaded cap 80. As detailed in FIG. 2B, the nested region shouldcomplement a portion of the curvature of the outer surface of cap head82 such that the cap head 82 sits snugly within the depressed orcountersunk rim 30 of the elongated aperture 26. The nested region 32with its surface features, i.e., notches 34, helps to avoid any slidingor migration of the bone screw 40 within the elongate slot.

FIG. 3 also depicts an approach for applying the same bone plate andbone screw system 10 of the present invention. In this procedure, bonescrews 40 are first applied to the bone segments to be fixed, using aconventional bone screw insertion tool such as insertion tool 100 whichhas a threaded tip for engaging the threaded bore 68 of the bone screws40. Preferably, each of the screws 40 is already engaged to theinsertion tool 100 prior to assembly. As shown in FIG. 3, the insertiontool 100 can also include an enlarged tapered head 102 so that the tool100 can also serve as an expansion post. The tool 100 can bepreassembled with the screw 40, and the entire tool-screw combinationcan be placed within a cannulated instrument to be applied all at once.Alternatively, the bone screws 40 can be inserted into the bone segmentsto be fixed, and posts attached to their threaded bores 68 afterwards.Once the posts are in place, the bone plate 20 can then be placed overthe bone screws 40, using the posts for aligning the apertures 26 overthe implanted bone screws 40. The locking members 70 can already becaptured within the seating groove 28 of each of the apertures 26 of theplate 20 prior to assembly. After the bone plate 20 is positioned overthe implanted bone screw or screws 40, the plate 20 and the capturedlocking members 70 are slid down and over the enlarged tapered head 102.The tapered head 102, which has a maximum outer diameter larger than theresting inner diameter of the resilient locking member 70, willfacilitate the expansion of the C-ring and enable the resilient lockingmember 70 to expand and slide over the top flange 48, then contract andsnap back to nest within the groove 60 of the bone screw 40. Oncedisposed around groove 60 and captured within the seating groove 28 ofthe apertures 26, the resilient locking member 70 secures the bone plate20 to the implanted bone screws 40. At this point, the bone screws 40can be completely threaded into the bone segments, if they have notalready been done so. Finally, threaded cap 80 can be applied to thethreaded bore 68 of the bone screws 40 to further secure the bone plate20 to the now implanted bone screws 40.

The ability of the bone plate and bone screw system 10 to be assembledas either a plate first or anchors first approach provides the surgeonwith the flexibility to assemble the screw to the plate or the plate tothe screw, depending on the surgeon's preference and the particularcircumstances of the patient. By providing the surgeon with differentassembly techniques, the present invention allows the surgeon more waysto align the bone plate and bone screws during surgery. Further throughuse of the optional threaded cap, the surgeon is provided with means toadjust the spacing between screws across the graft interface, e.g., toprovide and maintain compression across the graft interface to enhancethe environment to achieve bony fusion.

FIG. 4A illustrates another exemplary bone plate and screw system 110 inaccordance with the present invention, in which a bone plate 120 isprovided for assembly with bone screws 140 having non-resilient flanges148, 154. The bone plate 120 can be secured to the bone screws 140 usingresilient locking members 170. The bone screws 140 of this embodimentshare similar features to the bone screws 40 of system 10, while thebone plate 120 shares similar features to the bone plate 20 of system10; thus, similar elements are designated by the same number preceded bythe suffix “1.” One salient difference between the bone screws 40 ofsystem 10 and the bone screws 140 of system 110 is that the top flange148 of bone screws 140 is not chamfered. The bottom flange 154 of thebone screw is chamfered to accommodate a plate-first technique. However,in the assembly process which is described in detail below, taperedposts can be attached to the bone screws 140 to provide the chamferedsurface needed to facilitate the expansion of the resilient lockingmember 170 over the top flange 148 of the bone screws 140.

As shown, the resilient locking member 170 can include anexpandable/compressible C-ring which is configured to sit within thegroove 160 of the bone screw 140. The resilient locking member 170 isconfigured to also nest within seating groove 128 of the round aperture126 of the bone plate 120. For the oblong aperture 126 of the bone plate120, a second type of resilient locking member 170′ is provided.Resilient locking member 170′ can also be a split ring for snapping intothe groove 160 of the bone screw 140. The resilient locking member 170′also has enlarged end portions 174′, with at least one of the enlargedend portions 174′ including a notched edge 176′. As depicted in FIG. 4B,this notched edge 176′ is configured to mate and engage with a ratchetededge 134 running along a portion of the seating groove 128 of the oblongaperture 126. The ratcheted edge 134 enables the resilient lockingmember 170′ and the bone screw 140 attached therewith to be maintainedwithin the elongated aperture 126 to ratchet in discrete increments withrespect to the length of the aperture 126. Such features provide thesurgeon with even more flexibility with respect to the manner ofassembling the bone plate and screw system 110. These features alsoprovide a clinical benefit to maintain compression at the bone/graftinterface.

As in the previous embodiment, the bone plate and screw system 110 ofthe present invention can be assembled using either a plate first or ananchors first approach as described above. In an anchors first approachwhere the bone plate 120 is assembled to the implanted bone screws 140,the bone screws 140 are implanted into the bone segments to be fixed. Asshown in FIG. 5A, it is preferable to use a single bone screw 140 pervertebral body 5 to assist with proper alignment of the plate to thescrews. However, it is understood that any number of bone screws 140 canbe applied as deemed necessary by the surgeon, and as required by theparticular bone plate to be used. After the bone screws 140 are applied,tapered posts 104 can be attached to the bone screws 140 as shown inFIG. 5B. Alternatively, the tapered posts 104 can be pre-engaged to thescrews 140 prior to insertion. The tapered post 104 can extending into athickened region 106 having a screw-engaging tip for engagement with atool-engaging bore 168 extending from an upper surface of the top flange148 of the bone screws 140. The tapered posts 104 can be used to alignthe bone plate 120, with the resilient locking members 170, 170′captured within the seated grooves 132 of the bone plate 120, onto theimplanted bone screws 140, as illustrated in FIG. 6A. The thickenedregion 106 of the posts 104 helps facilitate the expansion of theresilient locking members 170, 170′ so that as the resilient lockingmembers 170, 170′ slide down the post 104, the C-rings gradually expandto slide over the top flanges 148 of the bone screws 140 and snap intotheir grooves 160. The resilient locking members 170, 170′, which arenested within seating grooves 128 of the bone plate, now surround thegrooves 160 of the bone screws 140 as depicted in FIG. 6C. After thebone plate 120 is sufficiently secured to the implanted bone screws 140,the posts can be removed to leave a fully assembled bone plate and screwsystem 110 as shown in FIG. 6B.

In another exemplary embodiment of the present invention, a bone screw240 and locking ring 270 is provided as shown in FIGS. 7A-7C, for usewith a bone plate such as the plate 20 of the system 10 previouslydescribed. Bone screw 240 is sized and shaped to be received within theapertures of the bone plate 20 to anchor the plate 20 to the particularbone segments that require fixation. Screw 240 has a head region 246 ata proximal end 242. The head region 246 is defined by an upper surface250, a lower surface 252, and a sidewall 254 extending therebetween andconnecting the upper and lower surfaces 250, 252. An elongated body 262which includes a threaded portion 264 extends from the head region 246to a distal end of the screw 240. As illustrated in FIGS. 7A and 7B, theupper surface 250 and the lower surface 252 of the head region 246 canbe chamfered.

The bone screw 240 cooperates with a resilient locking member 270 asshown in FIG. 7A for securing the bone plate 20 to the screw 240. Theresilient locking member 270 is sized and configured to be capturedwithin the seating groove 28 of the aperture 26 of the bone plate 20. Aswith locking member 70 of the previous system 10, resilient lockingmember 270 can be formed as a C-ring, or an expandable snap ring. Asshown in FIG. 7C, resilient locking ring 270 includes a top surface 280,a bottom surface 282, and an outer wall 284 extending therebetween andconnecting the top and bottom surfaces, 280, 282. Top surface 280 can beformed so as to extend along a downward slope from an outer edge to aninner edge of the top surface 280. Likewise, bottom surface 282 can beformed so as to extend along an upward slope from an outer edge to aninner edge of the bottom surface. The slopes of the top and bottomsurfaces 280, 282 help to facilitate insertion of the locking member 270into or onto the head region 246 of the bone screw 240.

A channel 286 extends about the inner circumference of the locking ring270. The channel 286 is sized and shaped to capture the head region 246of the screw 240, and is defined by a top side 290, a bottom side 292,and an inner wall 294 connecting the top and bottom sides together. InFIG. 7C, the top and bottom sides 290, 292 extend at right angles withrespect to the inner wall 294. Such a channel 286 provides for somemovement of the head region 246 within the channel 286 itself. However,it is understood that top and bottom sides 290, 292 can be formed atangles with respect to the inner wall 294, thereby forming a closer fitwith the bone screw 240 where the head region 246 includes chamferedsurfaces such as is shown in FIG. 7B. In another aspect of the presentinvention, bone screw 240′ can include a head region 246′ having asidewall 254′ which extends at a perpendicular angle with respect to theupper and lower surfaces 250′, 252′ as shown in FIG. 8B. As best seen inFIG. 8B, the head region 246′ of the bone screw 240′ would becomplementary in shape and size to the channel 286 of the resilientlocking member 270, enabling both screw 240′ and locking member 270 towork and cooperate in congruence together. Additionally, since theinterface between the two components is flat, i.e., direct, the overallstability and integrity of the system is enhanced. In both the bonescrews 240, 240′ just described, a tool-engaging bore 268 extending fromthe upper surface 250, 250′ of the screws can be provided, asillustrated in FIG. 8C.

While the bone plate and screw systems described above utilize aresilient locking member 70, 170, 270 to secure the screws to the plate,the present invention also provides a bone plate and screw system inwhich the bone screw itself is resilient. As illustrated in detail inFIGS. 9A-9C, a bone screw 340 is provided having a head region 346 at aproximal end 342 and an elongated body 362 extending from the headregion 346 to a distal end 344 of the screw 340. Elongated body 362includes a threaded portion 364 configured for insertion into bone. Thehead region 346 has a top flange 348, a bottom flange 354, and a groove360 located between the top and bottom flanges 348, 354 and extendingabout the circumference of the head region 346. Like bone screw 40, thetop flange 348 of screw 340 can include a chamfered upper surface 350and the bottom flange 354 can include a chamfered lower surface 358. Asshown in detail in FIG. 9B, each of the flanges 348, 354 are providedwith relief slits 366 extending therethrough, which allow the flanges348, 354 to have compressible diameters. The slits 366 can comprise anysuitable shape, including wavy S-shaped slits as shown. While the reliefslits 366 of the top flange 348 are illustrated in FIG. 9C as beingaligned with respect to the relief slits 366 of the bottom flange 354,it is contemplated that the relief slits 366 can be offset to provide amore robust system. Though not shown, it is also understood that thescrew 340 can include a tool-engaging bore such as with screw 40.

As with the previously described bone screws, bone screw 340 can be usedto secure a bone plate onto a bone segment to be fixed. The bone plateshould be of the type having a first surface, a second, bone-contactingsurface opposed to the first surface, and an aperture extending throughthe first and second surfaces. The aperture should be sufficiently sizedand shaped to receive the screw 340 and nest within the groove 360between the two flanges 348, 354. The resiliency of the flanges 348, 354enables bone screw 340 to be secured to a bone plate without the needfor a locking member in both a plate first or an anchors first approach.For instance, in an exemplary method of using bone screw 340, the screw340 can be inserted into a bone segment to be fixed in an anchors firstapproach. To allow for an anchors fist approach, at least the top flangeof the bone screw should be resilient. Next, the aperture of the boneplate can be placed over a post attached to the screw 340 to align thebone plate to the implanted screw 340. The optional post can be attachedto the screw 340 prior to or after insertion into the bone segment toassist with alignment of the screw to the aperture of the plate. Afterthe aperture is disposed over the post, the bone plate is slid down thepost and onto the screw. The flexibility of the top flange 348 enablesthe aperture to move over the flange 348 and nest within the groove 360of the screw 340. Once the aperture is secured around the screw 340, thepost can be removed from the screw.

Alternatively, the present system can also utilize an optionalattachment member and a bone plate having a seating groove such as boneplate 20 described above. The attachment member helps to facilitate theengagement and cooperation of the bone screw 340 and the bone plate. Theattachment member should be configured to nest within the seating groove28 of the bone plate 20 and seat around the groove 360 of the screw 340.Preferably, the attachment member would be captured within the seatinggroove 28 of the bone plate 20 prior to assembly so that the step ofsecuring the aperture 26 around the screw 340 would include securing thecaptured attachment member around the groove 360 of the bone screw 340.While not illustrated, it is contemplated that the attachment member caninclude a notched edge such as with locking member 170′. The seatinggroove of the bone plate can also include a ratcheted edge along itsside to allow the notched edge of the attachment member to mate andincrementally move within the aperture itself. If desired, a threadedcap 80 can be attached to the bone screw 340 to limit movement of thescrew 340 within the aperture 26 in the same manner described above.

FIGS. 10A-10F illustrate yet another embodiment of a bone screw 440 andlocking member 470 of the present invention. Bone screw 440 includes ahead region 446 at a proximal end 442 and an elongated body 462extending from the head region 446 to a distal end 444 of the screw 440.The elongated body 462 includes a threaded portion 464 configured forinsertion into bone. The head region 446 includes an upper surface 450,a lower surface 452, and a sidewall 454 extending therebetween andconnecting the upper and lower surfaces 450, 452. As illustrated in FIG.10C, the sidewall 454 can extend at a perpendicular angle with respectto the upper and lower surfaces 450, 452. FIG. 10B shows a similar bonescrew 440′ where the upper and lower surfaces 450, 452 are chamfered.Both screws 440, 440′ are provided with relief slits 466, 466′ thatextend through the head region 446 to provide it with a compressiblediameter. The slits 466 can comprise any suitable shape, including wavyS-shaped slits as shown. While it is not shown, it is understood thatthese bone screws 440, 440′ can be provided with a tool-engaging recessand/or tool-engaging bore for attaching an insertion tool thereto.

Bone screw 440 can be used to secure a bone plate onto a bone segment tobe fixed. The bone plate should be of the type having a first surface, asecond, bone-contacting surface opposed to the first surface, and anaperture extending through the first and second surfaces. The apertureshould be sufficiently sized and shaped to receive the screw 440 andalso include a seating groove to capture the head region 446 of thescrew 440. Preferably, the aperture of the bone plate should becountersunk on at least one of the first and second surfaces toaccommodate and facilitate the engagement of the screw with the boneplate. The resiliency of the head region 446 enables bone screw 440 tobe secured to a bone plate without the need for a locking member in botha plate first or an anchors first approach. For instance, in anexemplary method of using bone screw 440, the screw 440 can be insertedinto a bone segment to be fixed in an anchors first approach. Next, theaperture of the bone plate can be placed over a post attached to thescrew 440 to align the bone plate to the implanted screw 440. The postcan be attached to the screw 440 prior to or after insertion into thebone segment. After the aperture is disposed over the post, the boneplate is slid down the post and onto the screw 440. The compressibilityof the head region 446 enables the aperture to move over the head region446. Once the head region 446 is captured within the seating groove ofthe bone plate, the post can be removed from the screw.

However, as shown in FIGS. 10A and 10D-10F, the bone screw 440 can beused in combination with an optional attachment member 470. Theattachment member 470 helps to facilitate the engagement and cooperationof the bone screw 440 and the bone plate. Preferably, the attachmentmember 470 is similar to the locking member 270 shown in FIG. 7C but isa closed ring rather than a C-ring. The attachment member 470 can becaptured within the seating groove of the bone plate prior to assemblyso that placement of the aperture over the post also aligns the capturedattachment member with the implanted screw 440. Once the attachmentmember 470 is moved down and over the resilient head region 446, thehead region 446 can nest within the groove of the attachment member 470,as shown in FIGS. 10E and 10F. By providing a flat, complementaryinterface between the attachment member 470 and the head region 446 asdetailed in FIG. 11C, the congruency and integrity of the interferencefit is maintained. If desired, a threaded cap can be attached to thescrew to limit its movement within the aperture.

The present invention also provides a bone plate and screw system inwhich the plate itself is resilient. As illustrated in FIGS. 11A and11B, bone plate 520 has a resilient aperture 528 for use with anon-resilient bone screw for stabilizing bone segments to be fixed. Thebone plate 520 includes a body 522 defined by a first surface 524, asecond, bone-contacting surface 526 opposed to the first surface 524,and a resilient aperture 528 extending through the first and secondsurfaces 524, 526 whose material resilience enables bi-directionalassembly of a bone screw and the bone plate 520. The aperture 528 issized and configured to receive a bone screw such as exemplary bonescrew 502 as shown in FIGS. 11C-11E. As illustrated in detail in FIG.11D, bone screw 502 includes a proximal end 504, a distal end 506, ahead region 512 defined by a flange 514, a groove 516 extending aboutthe circumference of the head region 512, and a body 508 extend from thegroove 516. The body 508 includes a threaded portion 510 configured forinsertion into bone. The aperture 528 can be countersunk from a firstsurface 524 of the bone plate. The countersunk portion 534 of theaperture 528 can extend toward the second, bone-contacting surface 526of the bone plate 520. As shown in FIG. 11E, the groove 516 of bonescrew 502 is configured to mate with the aperture 528 of the resilientbone plate 520, while the flange 514 is configured to seat against thecountersunk region 534 of the aperture 528.

To facilitate the opening of the aperture 528, a relief slit 538 isprovided. The relief slit 538 extends through the first and secondsurfaces 524, 526 of the plate 520, and extends from the aperture 528 toa through-hole, or relief hole 540. The relief slit 538 and relief hole540 provide the aperture 528 with the ability to expand and contract. Asshown in FIG. 11B, the slit 538 can extend longitudinally through thebone plate 520. Plate 520 can be concavely curved along its longitudinalaxis to provide a better fit with the natural contours of human bones.The body 522 can be defined by a pair of longitudinal sidewalls 530connected by a pair of opposed lateral endwalls 532. As illustrated, amidsection of each of the longitudinal sidewalls extends 530 towards acentral region of the body 522. Similarly, a midsection of each of thelateral endwalls 532 extends towards a central region of the body 522.This provides the body 522 with a shape similar to a bowtie. Theaperture 528 can be configured as either a slot (as shown) to allowtranslation of the screw, or as a hole to provide a rigid fixed positionfor the screw within the plate.

FIGS. 12A and 12B illustrate another variation of the resilient boneplate of the present invention, in which the aperture 528′ of bone plate520′ can also include a countersunk portion 536′ from the second surface526′ of the plate 520′. In all other respects, the bone plate 520′ shownis similar to the bone plate 520 previously described, with commonfeatures designated by the same numeral followed by the symbol “′.” Theresilient bone plate 520′ of the present invention can be applied usinga bone screw similar to the one illustrated in FIGS. 1A-1C, anddescribed above as bone screw 40. FIGS. 12C-12E illustrate the boneplate 520′ assembled with an exemplary bone screw 40. As shown in detailin FIG. 12E, the aperture 528′ is sized and shaped to directly engagethe groove 60 of the bone screw 40 for locking engagement.

Consistent with all of the bone plate and screw systems of the presentinvention, the flexibility of the aperture 528′ enables the bone plate520′ to be assembled to bone screw 40 in either a plate first or ananchors first approach. To apply the bone plate 520′ in an anchors firstapproach, the bone screw 40 can be inserted into the bone segment to befixed. Using a post attached to the bone screw 40 as an alignment guide,the aperture 528 can be placed onto the post and slid down. The post canbe attached either prior to or after insertion of the screw 40 into thebone segment. Preferably, the post can be tapered. As the plate 20 isslid down the post, the taper of the post opens up the resilientaperture 528′, allowing the aperture 528′ to move over the top flange 48and snap into the groove 60 of the bone screw 40 as shown in FIG. 12E.Once the plate 520′ is secured around the screw 40, the post can beremoved. It is contemplated that the countersunk portion 534′ can alsoinclude a nesting region similar to the one for bone plate 20. Ifdesired, a threaded cap can be attached to the screw 40 to restrictmovement of the screw 40 within the aperture 528′.

While described and illustrated with bone screw 40 having two flanges,it is understood that the resilient bone plate 520 of the presentinvention can be provided with a seating groove around the aperture 528.Such a feature would enable the bone plate 520 to be used with a bonescrew having a single flange, similar to the bone screw 240′ illustratedin FIG. 8A. Optionally, a locking member such as locking member 270 canbe used with bone screw 240′ to secure the bone plate 520 to theimplanted bone screw.

FIGS. 13A and 13B illustrate yet more configurations for the resilientbone plate of the present invention, in which the resilient bone platecomprises a plurality of apertures, relief slits, and relief holes. Asshown, bone plate 620 can be defined by a pair of longitudinal sidewalls630 connected by a pair of opposed lateral endwalls 632. The bone plate620 can include a plurality of apertures 628 connected together by arelief slit 638 which terminates into a pair of relief holes 640 asshown in FIG. 13A. An alternative pattern is shown in FIG. 13B, in whichbone plate 620′ can include a pair of longitudinal sidewalls 630′connected by a pair of opposed lateral endwalls 632′. Bone plate 620′includes a pair of relief slits 638′, each relief slit 638′ extendinginto at least one relief hole 640′ and an aperture 628′.

Yet more configurations are illustrated in FIGS. 14A and 14B, in which aresilient bone plate 720 and a resilient bone plate 820 are shown.Resilient bone plate 720 includes a pair of lateral sidewalls 730connected by a pair of opposed lateral endwalls 732. Relief slits 738extend along the lateral endwalls 732, each relief slit 738 terminatingat each end into an aperture 728. In FIG. 14B, resilient bone plate 820includes a single relief slit 538 extending into apertures 828 at eachterminal end. The aperture can be configured as either a slot to allowtranslation of the screw, or as a hole to provide a rigid fixed positionfor the screw within the plate. As shown, resilient bone plate 820includes apertures 828 having both shapes.

All of the bone plate and screw systems of the present invention can beassembled together using either a plate first or an anchors firstapproach, with the latter approach being desirable to provide thebenefits accorded with an anchors first approach as previouslymentioned. Preferably, the system can be assembled bi-directionallyusing both a plate first and an anchors first construction. It isunderstood that the components of the systems of the present inventioncan be formed from any biocompatible material, including biocompatiblemetals and polymers. It is also contemplated that the components canequally comprise bioabsorbable and/or biodegradable materials. Likewise,all components are considered to require dimensions suitable for use asmedical implants.

It will be understood that the foregoing is only illustrative of theprinciples of the invention, and that various modifications can be madeby those skilled in the art without departing from the scope and spiritof the invention. All references cited herein are expressly incorporatedby reference in their entirety.

1. A bone plate and resilient screw system for the stabilization of bonesegments, comprising: a bone plate having a first surface, a second,bone-contacting surface opposed to the first surface, and an apertureextending through the first and second surfaces, the aperture having apredefined shape and size, and being configured to receive a bone screw;and a resilient screw configured to be inserted into bone, the screwhaving a head region at a proximal end, the head region being defined bya top flange, a bottom flange, and a groove extending therebetween, andan elongated body extending from the head region to a distal end of thescrew, the elongated body including a threaded portion; wherein at leastone of the top and bottom flanges includes at least one curved reliefslit extending non-radially into the flange such that the relief slitseparates the flange into an outer peripheral portion and an innerportion such that at least one of the top and bottom flanges of thescrew is resilient.
 2. The system of claim 1, wherein both the top andbottom flanges are resilient.
 3. The system of claim 1, wherein therelief slit is S-shaped.
 4. The system of claim 1, wherein a proximalsurface of the top flange is chamfered.
 5. The system of claim 1,wherein a distal surface of the bottom flange is chamfered.
 6. Thesystem of claim 1, wherein the aperture of the bone plate furtherincludes a seating groove therein.
 7. The system of claim 6, furtherincluding an attachment member for securing the bone plate to the screw,the attachment member being configured to be captured within the seatinggroove of the aperture, and further being sized and shaped to mate withthe groove of the screw.
 8. The system of claim 7, wherein theattachment member is a closed ring.
 9. The system of claim 1, whereinthe screw has an open head region, the region including a tool-engagingbore extending from an upper surface thereof.
 10. The system of claim 9,wherein the tool-engaging bore is a threaded bore.
 11. The system ofclaim 9, wherein the tool-engaging bore is a hexagonal bore.
 12. Thesystem of claim 9, further including a cap configured to engage thetool-engaging bore.
 13. The system of claim 12, wherein the capcomprises a head region and a threaded body extending therefrom.
 14. Thesystem of claim 12, wherein the cap further includes a tool-engagingbore extending from an upper surface of the head region.
 15. The systemof claim 12, wherein the aperture includes a countersunk rim on thefirst surface of the bone plate.
 16. The system of claim 15, wherein thecountersunk rim includes a nested region for capturing the cap.
 17. Thesystem of claim 16, wherein the nested region includes surface featuresto restrict movement of the cap.
 18. The system of claim 16, wherein thecap restricts translation and/or rotation of the screw with respect tothe aperture.
 19. The system of claim 1, wherein the predefined shape ofthe aperture is selected from the group consisting of a hole and anoblong slot.